Silicone compositions are excellent in heat resistance, cold resistance, weather resistance, light resistance, chemical stability, electric properties, flame retardancy, water resistance, transparency, coloring properties, non-cohesiveness, and non-corrosiveness and are used in various industries, but have the disadvantage of low strength. Although silica is generally added for improving the strength, there occurs the problem of opacifying the compositions or increasing specific gravities. Also, it is known that silicone rubber powder, polyorganosilsesquioxane powder, or silicone rubber powder coated with polyorganosilsesquioxane is added for improving the strength. However, the strength improving effect is not sufficient, and, particularly, there is the problem of adversely affecting transparency due to the large particle diameter (refer to, for example, Patent Documents 1 to 3).
Further, a rubber portion of silicone rubber powder or silicone rubber powder coated with polyorganosilsesquioxane is prepared by crosslinking with addition reaction of vinyl group-containing polyorganosiloxane and hydrogen organopolysiloxane in the presence of a platinum catalyst. However, this method has the problem of difficulty in synthesizing small particles having a particle diameter of 1 μm or less and difficulty in controlling the particle diameter. In addition, the method is economically disadvantageous because an expensive platinum catalyst is used (refer to, for example, Patent Document 2).
As described above, in the present situation, there is demand for an additive capable of increasing the strength of silicone compositions and maintaining transparency.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2-163127
Patent Document 2: Japanese Patent No. 2832143
Patent Document 3: Japanese Unexamined Patent Application Publication No. 7-150047